Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.79   13.114%   $236.1707   $236.17   $236.15   $236.20  
  Purchase #2 $85.54   7.190%   $91.6903   $91.69   $91.70   $91.70  
  Purchase #3 $165.29   9.165%   $180.4388   $180.44   $180.45   $180.40  
  Purchase #4 $207.86   4.495%   $217.2033   $217.20   $217.20   $217.20  
  Purchase #5 $239.43   3.574%   $247.9872   $247.99   $248.00   $248.00  
  Purchase #6 $238.89   5.654%   $252.3968   $252.40   $252.40   $252.40  
  Purchase #7 $233.54   8.808%   $254.1102   $254.11   $254.10   $254.10  
  7 purchase totals = $1,379.34       $1,479.9973   $1,480.00   $1,480.00   $1,480.00